Just some old leaded paint we found in gandpappys shed

Simply search for food coloring pens. Patisserie shops sell them, and so does Amazon, but I wouldn't draw on a kid's banana with a random pen ordered off of Amazon, unless it's a reputable brand.

Probably paint pens like Poscas.

You can use the tip of a kitchen knife or a hobby knife to etch a message into the skin. The cuts will turn brown quickly.

Oil pastel maybe? Would work if you plastic wrap it after.